This research plan is guided by two goals: (a) to determine if cognitive activities known to modulate cerebral hemovelocity in young adults induce comparable changes in older, stroke-free persons, and (b) to document time-course modulations in hemovelocity that emerge while older persons perform these activities. These goals lead to two specific objectives: (1) verify the effects of individual cognitive activities or. the velocities of younger persons, and (2) document the effects of the same cognitive activities on velocities of older, stroke-free persons. To accomplish these objectives, three experiments will use a transcranial Doppler neuroimaging procedure to record bilateral cerebral blood flow velocity simultaneously while persons perform cognitive activities. The cognitive tasks model day-to- day thinking activities and will be selected from short-term remembering, envisaging a persona experience, making decisions, studying stimuli, and solving problems that are language based, nonlanguage based, or quantitative. Two experiments will follow two-way factorial designs, with repeated measures on insonation side (right and left) and cognitive phases (relevant baselines and specific tasks). The middle cerebral artery of young adults (Experiment 1) and older, stroke-free persons (Experiment 2) will be sampled while they perform 7-to-9, 31-sec cognitive tasks within. a 30-min test session. The third experiment will expand to a three-way factorial design by adding cerebral arteries (middle, anterior, posterior) as a factor. The arteries of the same older, stroke-free persons will be sampled to compare relative velocity differences that may emerge during the cognitive activities. Attainment of the two goals will provide a repertoire of cognitive probes to practitioners serving as adjuncts to traditional functional tests in assessing the temporal resiliency to the cerebrovascular autoregulation mechanisms of older persons, including those who may show cerebrovascular dysfunction.